Magnetic random access memory and method of manufacturing the same

ABSTRACT

A magnetic random access memory includes a first wiring, a second wiring formed above and spaced apart from the first wiring, a magnetoresistive effect element formed between the first wiring and the second wiring, formed in contact with an upper surface of the first wiring, and having a fixed layer, a recording layer, and a nonmagnetic layer formed between the fixed layer and the recording layer, a metal layer formed on the magnetoresistive effect element and integrated with the magnetoresistive effect element to form stacked layers, a first side insulating film formed on side surfaces of the metal layer, the magnetoresistive effect element, and the first wiring, a first contact formed in contact with a side surface of the first side insulating film, and a third wiring formed on the metal layer and the first contact to electrically connect the magnetoresistive effect element and the first contact.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 11/839,265 filed Aug. 15, 2007,and claims the benefit of priority under 35 U.S.C. §119 from JapanesePatent Application No. 2006-269334 filed Sep. 29, 2006, the entirecontents of each of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic random access memory (MRAM)using the magnetoresistive effect, and a method of manufacturing thesame.

2. Description of the Related Art

Recently, many types of memory for storing information by theapplication of new principles have been proposed. One such type, asproposed by Roy Scheuerlein et al., is the magnetic random access memoryusing the tunneling magnetoresistive (TMR) effect. (See non-patentreference 1.)

A magnetic random access memory stores a binary value in a magnetictunnel junction (MTJ) element. The MTJ element has a structure in whichtwo magnetic layers (ferromagnetic layers) sandwich an insulating layer(tunnel barrier). Whether value stored in the MTJ element is binary 1 or0 is determined in accordance with whether the spin directions in thetwo magnetic layers are parallel or antiparallel.

Data written in the MTJ element is read as follows. Switching elementsare connected in series with MTJ elements, and only a switching elementconnected to a selected read word line is turned on to form a currentpath. Since a current flows to only the selected MTJ element, data canbe read from the MTJ element.

When a MOSFET is used as the switching element, the cell size is 12F² ifthe short side (the width in the magnetic hard axis direction) of theMTJ element is F (Feature size) and the long side (the width in themagnetic easy axis direction) is 2F. Accordingly, the cell size of themagnetic random access memory is larger than those of a DRAM and flashmemory. The cell size becomes 10F², therefore, if an easy axis write bitline is formed below the MTJ element and the lower electrode of the MTJelement and the fringe of the contact of the lower electrode areself-aligned. However, the decrease in cell size is stillunsatisfactory.

[Non-patent reference 1] Roy Scheuerlein et al., ISSCC2000 TechnicalDigest p. 128, “A 10 ns Read and Write Non-Volatile Memory Array Using aMagnetic Tunnel Junction and FET Switch in each Cell”

[Patent reference 1] Jpn. Pat. Appln. KOKAI Publication No. 2005-175357

BRIEF SUMMARY OF THE INVENTION

A magnetic random access memory according to the first aspect of thepresent invention comprises a first wiring, a second wiring formed aboveand spaced apart from the first wiring, a magnetoresistive effectelement formed between the first wiring and the second wiring, formed incontact with an upper surface of the first wiring, and having a fixedlayer, a recording layer, and a nonmagnetic layer formed between thefixed layer and the recording layer, a metal layer formed on themagnetoresistive effect element and integrated with the magnetoresistiveeffect element to form stacked layers, a first side insulating filmformed on side surfaces of the metal layer, the magnetoresistive effectelement, and the first wiring, a first contact formed in contact with aside surface of the first side insulating film, and a third wiringformed on the metal layer and the first contact to electrically connectthe magnetoresistive effect element and the first contact.

A magnetic random access memory according to the second aspect of thepresent invention comprises a first wiring, a second wiring formed aboveand spaced apart from the first wiring, a magnetoresistive effectelement formed between the first wiring and the second wiring, connectedto the second wiring, and having a fixed layer, a recording layer, and anonmagnetic layer formed between the fixed layer and the recordinglayer, a first side insulating film formed on a side surface of thefirst wiring, a first top insulating film formed on an upper surface ofthe first wiring, and a first contact formed below the magnetoresistiveeffect element, having a side surface in contact with a side surface ofthe first side insulating film, and electrically connected to themagnetoresistive effect element.

A magnetic random access memory manufacturing method according to thethird aspect of the present invention comprises forming a switchingelement on a semiconductor substrate, forming a first wiring above theswitching element, forming, on the first wiring, a magnetoresistiveeffect element having a fixed layer, a recording layer, and anonmagnetic layer formed between the fixed layer and the recordinglayer, forming a metal layer on the magnetoresistive effect element,forming a first side insulating film on side surfaces of the firstwiring, the magnetoresistive effect element, and the metal layer,forming a first interlayer insulating film covering the metal layer,exposing the metal layer by planarizing the first interlayer insulatingfilm, forming a contact hole which exposes a portion of the first sideinsulating film, forming, in the contact hole, a first contactconnecting to the switching element, forming a second wiring on thefirst contact and the metal layer to electrically connect the metallayer and the switching element by the second wiring, forming a secondinterlayer insulating film on the second wiring, and forming a thirdwiring on the second interlayer insulating film.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a sectional view showing a basic example of a magnetic randomaccess memory according to the first embodiment of the presentinvention;

FIG. 2A is a plan view showing the periphery of an MTJ element accordingto the first embodiment of the present invention;

FIG. 2B is a plan view showing the periphery of a gate electrodeaccording to the first embodiment of the present invention;

FIGS. 3 to 9 are sectional views showing the manufacturing steps of thebasic example of the magnetic random access memory according to thefirst embodiment of the present invention;

FIG. 10 is a sectional view showing a modification example of themagnetic random access memory according to the first embodiment of thepresent invention;

FIG. 11 is a sectional view showing the manufacturing step, followingFIG. 5, of the modification example of the magnetic random access memoryaccording to the first embodiment of the present invention;

FIG. 12 is a sectional view showing the manufacturing step, followingFIG. 11, of the modification example of the magnetic random accessmemory according to the first embodiment of the present invention;

FIG. 13 is a sectional view showing the MTJ element according to thefirst embodiment of the present invention;

FIG. 14A is a view showing the parallel arrangement of a parallelmagnetization type MTJ element according to the first embodiment of thepresent invention;

FIG. 14B is a view showing the antiparallel arrangement of the parallelmagnetization type MTJ element according to the first embodiment of thepresent invention;

FIG. 15A is a view showing the parallel arrangement of a perpendicularmagnetization type MTJ element according to the first embodiment of thepresent invention;

FIG. 15B is a view showing the antiparallel arrangement of theperpendicular magnetization type MTJ element according to the firstembodiment of the present invention;

FIG. 16 is a sectional view showing a basic example of a magnetic randomaccess memory according to the second embodiment of the presentinvention;

FIG. 17A is a plan view showing the periphery of an MTJ elementaccording to the second embodiment of the present invention;

FIG. 17B is a plan view showing the periphery of a gate electrodeaccording to the second embodiment of the present invention;

FIGS. 18 to 22 are sectional views showing the manufacturing steps ofthe basic example of the magnetic random access memory according to thesecond embodiment of the present invention;

FIG. 23 is a sectional view showing modification example 1 of themagnetic random access memory according to the second embodiment of thepresent invention;

FIGS. 24 to 28 are sectional views showing the manufacturing steps ofmodification example 1 of the magnetic random access memory according tothe second embodiment of the present invention;

FIG. 29 is a sectional view showing modification example 2 of themagnetic random access memory according to the second embodiment of thepresent invention;

FIG. 30 is a sectional view showing a magnetic random access memoryaccording to the third embodiment of the present invention;

FIGS. 31 to 33 are sectional views showing magnetic random accessmemories according to the third embodiment of the present invention;

FIGS. 34 and 35 are sectional views showing magnetic random accessmemories according to the fourth embodiment of the present invention;

FIGS. 36A to 36C are schematic sectional views showing magnetic randomaccess memory manufacturing steps using a via hole process according tothe fifth embodiment of the present invention; and

FIGS. 37A to 37D are schematic sectional views showing magnetic randomaccess memory manufacturing steps using a dual damascene processaccording to the fifth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will be explained below withreference to the accompanying drawing. The same reference numeralsdenote the same parts throughout the drawing.

[1] First Embodiment [1-1] Basic Example of a Magnetic Random AccessMemory

FIG. 1 is a sectional view showing a basic example of a magnetic randomaccess memory according to the first embodiment of the presentinvention. FIG. 2A is a plan view showing the periphery of an MTJelement according to the first embodiment of the present invention. FIG.2B is a plan view showing the periphery of a gate electrode according tothe first embodiment of the present invention. The basic example of themagnetic random access memory according to the first embodiment will beexplained below.

As shown in FIG. 1, a gate electrode 13 is formed on a semiconductorsubstrate 11 via a gate insulating film 12. Source/drain diffusionlayers 15 are formed in the semiconductor substrate 11 on the two sidesof the gate electrode 13, thereby forming a metal oxide semiconductor(MOS) transistor Tr as a switching element. Side insulating films 16 areformed on the side surfaces of the gate electrode 13, and a topinsulating film 14 is formed on the upper surface of the gate electrode13. The gate electrode 13 functions as a read word line RWL.

A contact 18 is connected to each source/drain diffusion layer 15. Thecontact 18 is formed in self-alignment with the gate electrode 13 andside insulating film 16. Therefore, the contact 18 is in direct contactwith the side surface of the side insulating film 16. A portion of thecontact 18 covers the upper portion of the side insulating film 16.

A write word line WWL is formed above the gate electrode 13. An MTJelement MTJ is formed on the write word line WWL. A conductive hard maskHM (metal layer) is formed on the MTJ element MTJ so as to be integratedwith it to form stacked layers. The planar shape of the hard mask HM is,for example, the same as that of the MTJ element MTJ. The side surfacesin the magnetic easy axis direction of the MTJ element MTJ are alignedwith the side surfaces of the hard mask HM and bit lint BL. Sideinsulating films 24 are formed on the side surfaces of the hard mask HM,the side surfaces in the magnetic easy axis direction of the MTJ elementMTJ, and the side surfaces of the write word line WWL.

A wiring 27 is formed on the hard mask HM. A contact 26 is formed belowthe wiring 27. The contact 26 is formed in self-alignment with the hardmask HM, MTJ element MTJ, write word line WWL, and side insulating film24. Accordingly, the contact 26 is in direct contact with the sidesurface of the side insulating film 24. A portion of the contact 26covers the upper portion of the side insulating film 24. One sidesurface in the magnetic easy axis direction of the wiring 27 is alignedwith the side surface of the contact 26, and the other side surface isaligned with the side surface of the side insulating film 24. A bit lineBL is formed above the MTJ element MTJ so as to be spaced apart from thewiring 27.

Desirable examples of the material of the hard mask HM are metals (forexample, Ru) that remain conductive even when oxidized, refractorymetals (for example, Ta, Ti, and W) that relatively stably remainconductive even when oxidized, and refractory metal compounds (forexample, TiN, TaN, and WN) having high oxidation resistance.

The material of the side insulating film 24 is desirably different fromthat of an interlayer insulating film 25. This is to increase theetching selectivity between the two materials during the formation ofthe contact 26. For example, when the interlayer insulating film 25 issilicon oxide (SiO₂), the side insulating film 24 is preferably siliconnitride (SiN) or alumina (AlxOy).

The material of the side insulating film 16 and top insulating film 14is desirably different from that of an interlayer insulating film 17.This is to increase the etching selectivity during the formation of thecontact 18. For example, when the interlayer insulating film 17 is SiO₂,the side insulating film 16 and top insulating film 14 are preferablySiN or AlxOy. Note that the side insulating film 16 and top insulatingfilm 14 are desirably the same material in view of the adhesion of thematerial and the like, but they may also be different materials.

The thickness Tt1 of the top insulating film 14 is desirably greaterthan the thickness Ts1 of the side insulating film 16. This is to allowthe top insulating film 14 to adequately protect the upper end portionand the like of the gate electrode 13 from being etched away during theformation of the contact 18.

The relationship between the film thickness Tt1 of the top insulatingfilm 14 and the film thickness Ts1 of the side insulating film 16desirably satisfies, for example, Tt1×⅓≦Ts1≦Tt1×½. The lower limit ismainly defined on the basis of the etching selectivity during theformation of the contact 18 and the insulation breakdown voltage. Theupper limit is defined so as to ensure a minimum necessary width of thecontact hole (particularly, the side width of the contact hole) when thecontact 18 is formed by etching.

The film thickness of the side insulating film 16 is, for example, about10 to 50 nm. The film thickness of the side insulating film 24 is, forexample, about 10 to 50 nm. The film thicknesses of the side insulatingfilms 16 and 24 are adjusted by damage absorption during etching and thedielectric breakdown voltage.

FIGS. 3 to 9 are sectional views showing the manufacturing steps of thebasic example of the magnetic random access memory according to thefirst embodiment of the present invention. A method of manufacturing thebasic example of the magnetic random access memory according to thefirst embodiment will be explained below.

First, as shown in FIG. 3, element isolation regions STI having an STI(Shallow Trench Isolation) structure are formed in a semiconductorsubstrate (for example, a silicon substrate) 11. Then, a gate insulatingfilm 12 is formed on the semiconductor substrate 11, and a gateelectrode 13 made of polysilicon or the like is formed on the gateinsulating film 12. A top insulating film 14 is formed on the gateelectrode 13. The top insulating film 14 is, for example, SiN. Afterthat, the gate insulating film 12, gate electrode 13, and top insulatingfilm 14 are patterned into a desired shape. Subsequently, source/draindiffusion layers 15 are formed in the semiconductor substrate 11. Thegate electrodes 13 function as, for example, read word lines RWL.

As shown in FIG. 4, a side insulating film 16 is formed on thesemiconductor substrate 11 and top insulating films 14, and patterned toremain on the side surfaces of the gate insulating films 12, gateelectrodes 13, and top insulating films 14. The side insulating film 16is, for example, SiN.

As shown in FIG. 5, an interlayer insulating film 17 of SiO₂ or the likeis formed on the semiconductor substrate 11 and top insulating films 14.Contact holes are formed in the interlayer insulating film 17 byreactive ion etching (RIE) or the like, and filled with tungsten (W) orthe like to form contacts 18. Each contact 18 can be formed inself-alignment with the side insulating film 16 and gate electrode 13 byforming the contact hole so as to expose the side surface of the sideinsulting film 16.

As shown in FIG. 6, wirings 19 connecting to the contacts 18 are formedand buried with an interlayer insulating film 20. The interlayerinsulating film 20 is then planarized until the wirings 19 are exposed.Subsequently, an interlayer insulating film 21 of SiO₂ or the like isformed on the wirings 19 and interlayer insulating film 20. A wiring 22of, for example, AlCu is formed on the interlayer insulating film 21. AnMTJ element film 23 and hard mask HM are formed on the wiring 22. Afterthe hard mask HM is patterned, the wiring 22 and MTJ element film 23 arepatterned into a desired shape. In this manner, bit lines BL and MTJelements MTJ are formed.

As shown in FIG. 7, side insulating films 24 are formed on the sidesurfaces of the bit lines BL, MTJ elements MTJ, and hard masks HM. Theside insulating film 24 is, for example, SiN.

As shown in FIG. 8, an interlayer insulating film 25 of, for example,SiO₂ is formed to cover the hard masks HM, and planarized until the hardmasks HM are exposed. After that, contact holes are formed in theinterlayer insulating films 21 and 25 by RIE or the like, therebypartially exposing the side insulating films 24. In this step, the hardmasks HM are sometimes partially exposed when the contact holes areformed. Contacts 26 are formed by burying W or the like in the contactholes. The contacts 26 are connected to the wirings 19.

Since the side insulating film 24 (for example, an SiN film) and theinterlayer insulating film 25 (for example, an SiO₂ film) are ofdifferent materials, the etching selectivity between them is high. Eachcontact hole is formed adjacent to the MTJ element MTJ so as to exposethe side surface of the side insulating film 24. In this manner, thecontact 26 can be formed in self-alignment with the side insulating film24, write word line WWL, MTJ element MTJ, and hard mask HM.

As shown in FIG. 9, a wiring 27 is formed on the hard masks HM andcontacts 26, and patterned into a desired shape. The wirings 27electrically connect the hard masks HM and transistors Tr.

Finally, as shown in FIG. 1, the wirings 27 are buried with aninterlayer insulating film 28, and a wiring 29 having a desired shape isformed on the interlayer insulating film 28. The wiring 29 functions asa bit line BL.

[1-2] Modification Example of Magnetic Random Access Memory

FIG. 10 is a sectional view showing a modification example of themagnetic random access memory according to the first embodiment of thepresent invention. This modification example of the magnetic randomaccess memory according to the first embodiment will be explained below.

As shown in FIG. 10, the hard mask HM and wiring 27 need not be indirect contact with each other, but can also be connected via a contact32. In this case, a top insulating film 31 is desirably formed on theupper surface of the hard mask HM. This is to protect the hard mask HMand the MTJ element MTJ from being partially etched away during theformation of the contact 26.

The top insulating film 31 and a side insulating film 24 desirablyconsist of a material that increases the etching selectivity to theinterlayer insulating films 21 and 25 around them. Therefore, when theinterlayer insulating films 21 and 25 are, for example, SiO₂, the topinsulating film 31 and side insulating film 24 are preferably, forexample, SiN or AlxOy. Note that while the top insulting film 31 andside insulating film 24 are desirably the same material in view of theadhesion of the material and the like, they may also be differentmaterials.

The top insulating film 31 is desirably thicker than the side insulatingfilm 24. This is to allow the top insulating film 31 to adequatelyprotect the upper end portions and the like of the hard mask HM and MTJelement MTJ from being etched away during the formation of the contact26.

FIGS. 11 and 12 are sectional views showing the manufacturing steps ofthe modification example of the magnetic random access memory accordingto the first embodiment of the present invention. A method ofmanufacturing the modification example of the magnetic random accessmemory according to the first embodiment will be explained below.

First, after the steps shown in FIGS. 3 to 5 described above areperformed, as shown in FIG. 11, the wirings 19 connecting to thecontacts 18 are formed and buried with the interlayer insulating film20. The interlayer insulating film 20 is then planarized until thewirings 19 are exposed. Subsequently, the interlayer insulating film 21is formed on the wirings 19 and interlayer insulating film 20. Thewiring 22 made of, for example, AlCu is formed on the interlayerinsulating film 21. The MTJ element film 23 is formed on the wiring 22,and the hard mask HM is formed on the MTJ element film 23. A topinsulating film 31 is formed on the hard mask HM. The top insulatingfilm 31 consists of, for example, SiN. After that, the wiring 22, MTJelement film 23, hard mask HM, and top insulating film 31 are patternedinto a desired shape. In this way, the bit lines BL and MTJ elements MTJare formed. The side insulating films 24 are formed on the side surfacesof the bit lines BL, MTJ elements MTJ, hard masks HM, and top insulatingfilms 31. The side insulating film 24 consists of, for example, SiN.

As shown in FIG. 12, an interlayer insulating film 25 of SiO₂ or thelike is formed and selectively removed by RIE, and the top insulatingfilms 31 are also selectively removed by RIE. This forms contact holesthat expose the hard masks HM. Contacts 32 connecting to the MTJelements MTJ are formed by burying W or the like in these contact holes.After that, the contacts 26, wirings 27, and a bit line BL aresequentially formed following the same procedures as above.

The modification example as described above can achieve the same effectas in the structure shown in FIG. 1, and can also achieve the followingeffects by forming the contacts 32. That is, this modification examplecan make the contact area between the MTJ element MTJ (hard mask HM) andwiring 27 smaller than that in the structure shown in FIG. 1. Thisalleviates the influence of stress, and facilitates magnetic design. Itis also possible to suppress etching damage to the MTJ element MTJ whenthe wiring 27 is processed.

[1-3] MTJ Element (1) Structure

FIG. 13 is a sectional view of the MTJ element according to the firstembodiment of the present invention. This MTJ element will be explainedbelow.

As shown in FIG. 13, the MTJ element MTJ has a fixed layer PF in whichmagnetization is fixed in one axial direction, a recording layer FF inwhich magnetization reverses, a nonmagnetic layer NF sandwiched betweenthe fixed layer PF and recording layer FF, and an antiferromagneticlayer (not shown) that fixes magnetization in the fixed layer PF.

Each of the fixed layer PF and recording layer FF is not limited to asingle layer as shown in FIG. 13. For example, each of the fixed layerPF and recording layer FF may also be a stacked film made up of aplurality of ferromagnetic layers. At least one of the fixed layer PFand recording layer FF can have an antiferromagnetic coupling structurewhich includes three layers, i.e., a first ferromagneticlayer/nonmagnetic layer/second ferromagnetic layer, and in which thefirst and second ferromagnetic layers magnetically couple with eachother (interlayer exchange coupling) such that the magnetizationdirections in these layers are antiparallel, or a ferromagnetic couplingstructure in which the first and second ferromagnetic layersmagnetically couple with each other (interlayer exchange coupling) suchthat the magnetization directions in these layers are parallel.

The nonmagnetic layer NF is not limited to a single-junction structureincluding one nonmagnetic layer as shown in FIG. 13. For example, theMTJ element MTJ may also have a double-junction structure having twononmagnetic layers. The MTJ element MTJ having this double-junctionstructure has a first fixed layer, a second fixed layer, a recordinglayer formed between the first and second fixed layers, a firstnonmagnetic layer formed between the first fixed layer and recordinglayer, and a second nonmagnetic layer formed between the second fixedlayer and recording layer.

The planar shape of the MTJ element MTJ is not limited to a rectangleand can be variously changed. Examples are an ellipse, circle, hexagon,rhomb, parallelogram, cross, and bean (recessed shape). To decrease thecell size, however, the planar shape of the MTJ element MTJ ispreferably a rectangle of F (short side)×2F (long side).

The fixed layer PF, nonmagnetic layer NF, and recording layer FF of theMTJ element MTJ are simultaneously processed to have the same planarshape. However, the present invention is not limited to this embodiment.For example, it is also possible to give the fixed layer PF andnonmagnetic layer NF a rectangular shape and only the recording layer FFa cross shape.

(2) Materials

The following ferromagnetic materials are used as the materials of thefixed layer PF and recording layer FF. Favorable examples are Fe, Co,Ni, and their stacked films and alloys, magnetite having a high spinpolarization ratio, oxides such as CrO₂ and RXMnO_(3-y) (R; rare earthelement, X; Ca, Ba, and Sr), and Heusler alloys such as NiMnSb andPtMnSb. These magnetic materials can more or less contain nonmagneticelements such as Ag, Cu, Au, Al, Mg, Si, Bi, Ta, B, C, O, N, Pd, Pt, Zr,Ir, W, Mo, and Nb, provided that the materials do not looseferromagnetism.

As the material of the nonmagnetic layer NF, it is possible to usevarious dielectrics such as Al₂O₃, SiO₂, MgO, AlN, Bi₂O₃, MgF₂, CaF₂,SrTiO₂, and AlLaO₃. These dielectrics may have oxygen, nitrogen, andfluorine deficiencies.

When an insulator such as MgO (magnesium oxide) or AlO (aluminum oxide,for example, Al₂O₃) is used as the nonmagnetic layer NF, the MTJ elementMTJ has the TMR (Tunneling Magneto Resistive) effect. When a metal suchas Cu or Pt is used as the nonmagnetic layer NF, the MTJ element MTJ hasthe GMR (Giant Magneto Resistive) effect.

(3) Magnetization Arrangement

FIGS. 14A, 14B, 15A, and 15B are views showing parallel and antiparallelmagnetization arrangements of the MTJ element according to the firstembodiment of the present invention.

As shown in FIGS. 14A and 15A, the tunnel resistance of the nonmagneticlayer NF is a minimum when the magnetization directions in the fixedlayer PF and recording layer FF of the MTJ element MTJ are parallel (thesame). This state is regarded as, for example, a “1” state.

On the other hand, as shown in FIGS. 14B and 15B, the tunnel resistanceof the nonmagnetic layer NF is a maximum when the magnetizationdirections in the fixed layer PF and recording layer FF of the MTJelement MTJ are antiparallel (opposite). This state is regarded as, forexample, a “0” state.

Note that the magnetization stabilizing directions in the fixed layer PFand recording layer FF can be a parallel magnetization type, i.e.,parallel to the film surface as shown in FIGS. 14A and 14B, or aperpendicular magnetization type, i.e., perpendicular to the filmsurface as shown in FIGS. 15A and 15B.

[1-4] Write Method (1) Magnetic Field Write

When using magnetic field write as a write method, data write to the MTJelement MTJ is performed as follows.

A bit line BL and write word line WWL corresponding to the MTJ elementMTJ of a selected cell are selected, and write currents are supplied tothe selected bit line BL and write word line WWL. A synthetic magneticfield generated by the write currents is applied to the MTJ element MTJto make the magnetization directions in the MTJ element MTJ parallel orantiparallel.

For example, the write current in the bit line BL flows in onedirection, and the write current in the write word line WWL flows inboth directions. In this case, the magnetization direction in therecording layer of the MTJ element MTJ is changed by changing thedirection of the write current flowing through the write word line WWL.Note that the write current in the bit line BL may also flow in bothdirections.

(2) Spin-Transfer Write

Spin-transfer write will be explained below with reference to FIGS. 14Aand 14B. Note that the flow directions of electrons e1 and e2 are ofcourse opposite to those of electric currents.

First, as shown in FIG. 14A, when the write current is supplied from thefixed layer PF to the recording layer FF, electrons that arespin-polarized (to be referred to as spin-polarized electronshereinafter) e1 flow from the recording layer FF to the fixed layer PF.Electrons having spins parallel to the fixed layer PF are transmittedthrough it, and electrons having spins antiparallel to the fixed layerPF are reflected by it. Consequently, the magnetization directions inthe recording layer FF and fixed layer PF form an antiparallelmagnetization arrangement.

On the other hand, as shown in FIG. 14B, when the write current issupplied from the recording layer FF to the fixed layer PF,spin-polarized electrons e2 are injected from the fixed layer PF intothe recording layer FF. As a consequence, the magnetization directionsin the fixed layer PF and recording layer FF form a parallelmagnetization arrangement.

Note that data write to the MTJ element MTJ can also be performed bycombining (1) magnetic field write and (2) spin-transfer write.

[1-5] Read Method

Data read from the MTJ element MTJ is performed by applying a voltage(or current) between the write word line WWL and read word line RWL, anddetecting a current (or voltage) by a sense amplifier (not shown),thereby determining whether the MTJ element MTJ is in the “1” or “0”state.

The resistance is low if the magnetization arrangement in the MTJelement MTJ is parallel (for example, the “1” state), and high if themagnetization arrangement is antiparallel (for example, the “0” state).Accordingly, whether the MTJ element is “1” or “0” can be determined byreading the difference between these resistance values.

[1-6] Effect

The first embodiment described above forms the contact 26, whichconnects the MTJ element MTJ and switching element, in self-alignmentwith the write word line WWL and MTJ element MTJ, thereby implementingthe structure in which the contact 26 is in direct contact with the sideinsulating film 24 of the write word line WWL and MTJ element MTJ. Thatis, the first embodiment can decrease the cell size because the contact26 that connects the MTJ element MTJ and MOS transistor Tr can be formedadjacent to the MTJ element MTJ. More specifically, as shown in FIG. 2A,letting F (Feature size) be the short side (the width in the magnetichard axis direction) of the MTJ element MTJ and 2F be the long side (thewidth in the magnetic easy axis direction), a cell of 2F×4F=8F² can beimplemented. This makes it possible to decrease the cell size.

[2] Second Embodiment

In the first embodiment, the contact connecting to the switching elementis formed beside an MTJ element. The second embodiment further decreasesthe cell size by forming a contact connecting to a switching elementbelow the MTJ element.

[2-1] Basic Example of Magnetic Random Access Memory

FIG. 16 is a sectional view showing a basic example of a magnetic randomaccess memory according to the second embodiment of the presentinvention. FIG. 17A is a plan view showing the periphery of an MTJelement according to the second embodiment of the present invention.FIG. 17B is a plan view showing the periphery of a gate electrodeaccording to the second embodiment of the present invention. The basicexample of the magnetic random access memory according to the secondembodiment will be explained below.

As shown in FIG. 16, the difference of the second embodiment from thefirst embodiment is the peripheral structure of an MTJ element MTJexplained below.

A wiring 27 is formed on a contact 26 connecting to a source/draindiffusion layer 15 of a MOS transistor Tr. The MTJ element MTJ is formedin contact with the upper surface of the wiring 27. The MTJ element MTJhas the same planar shape as the wiring 27. The side surfaces in themagnetic easy axis direction of the MTJ element MTJ are aligned with theside surfaces in the magnetic easy axis direction of the wiring 27, andthe side surfaces in the magnetic hard axis direction of the MTJ elementMTJ are aligned with the side surfaces in the magnetic hard axisdirection of the wiring 27. A hard mask HM is formed on the MTJ elementMTJ, and a bit line BL is formed on the hard mask HM.

A write word line WWL is formed below the MTJ element MTJ so as to bespaced apart from the wiring 27. Side insulating films 42 are formed onthe side surfaces in the magnetic easy axis direction of the write wordline WWL, and a top insulating film 41 is formed on the upper surface ofthe write word line WWL. The contact 26 is formed in self-alignment withthe write word line WWL and side insulating film 42. Therefore, thecontact 26 is in direct contact with the side insulating film 42. Aportion of the contact 26 covers the upper portion of the sideinsulating film 42.

Adjacent MOS transistors Tr share a source contact 18 of contacts 18connected to the source/drain diffusion layers 15 of the MOS transistorsTr. Accordingly, the distance between adjacent gate electrodes 13 isabout the sum of the width of the contact 18 and the film thickness of aside insulating film 16.

The material of the side insulating film 42 and top insulating film 41is desirably different from that of an interlayer insulating film 25.This is to increase the etching selectivity between the two materialsduring the formation of the contact 26. For example, when the interlayerinsulating film 25 is SiO₂, the side insulating film 42 and topinsulating film 41 are preferably SiN or AlxOy. Note that the topinsulating film 41 and side insulating film 42 are desirably the samematerial in view of the adhesion of the material and the like, but theymay also be different materials.

The thickness Ts2 of the side insulating film 42 is, for example, about10 to 50 nm. The thickness Ts2 of the side insulating film 42 can beless than the thickness Tt2 of the top insulating film 41. For example,it is favorable to satisfy Tt2×⅓≦Ts2≦Tt2×½. The lower limit is mainlydefined on the basis of the etching selectivity during the formation ofthe contact 26 and the insulation breakdown voltage. The upper limit isdefined so as to ensure a minimum necessary width of the contact hole(particularly, the side width of the contact hole) when the contact 26is formed by etching.

FIGS. 18 to 22 are sectional views showing the manufacturing steps ofthe basic example of the magnetic random access memory according to thesecond embodiment of the present invention. A method of manufacturingthe basic example of the magnetic random access memory according to thesecond embodiment will be explained below.

First, contacts 18 are formed in self-alignment with side insulatingfilms 16 and gate electrodes 13 through the steps shown in FIGS. 3 to 5described previously.

As shown in FIG. 18, wirings 19 connecting to the contacts 18 are formedand buried with an interlayer insulating film 20. The interlayerinsulating film 20 is then planarized until the wirings 19 are exposed.Subsequently, an interlayer insulating film 21 of SiO₂ or the like isformed on the wirings 19 and interlayer insulating film 20. A wiring 22made of, for example, AlCu is formed on the interlayer insulating film21. A top insulating film 41 of, for example, SiN is formed on thewiring 22. After that, the wiring 22 and top insulating film 41 arepatterned into a desired shape, thereby forming write word lines WWL.

As shown in FIG. 19, a side insulating film 42 is formed on the topinsulating films 41 and interlayer insulating film 21. The sideinsulating film 42 is, for example, SiN.

As shown in FIG. 20, the side insulating film 42 is selectively removedby RIE or the like and left behind on the side surfaces of write wordlines WWL and top insulating films 41.

As shown in FIG. 21, an interlayer insulating film 25 is formed on thetop insulating films 41, side insulating films 42, and interlayerinsulating film 21, thereby covering the top insulating films 41. Theinterlayer insulating film 25 is, for example, SiO₂. The interlayerinsulating film 25 is then planarized by CMP or the like to expose thetop insulating films 41. In this step, the interlayer insulating film 25may sometimes partially remain on the top insulating films 41.Subsequently, contact holes are formed in the interlayer insulatingfilms 21 and 25 by RIE or the like, thereby partially exposing the sideinsulating films 42. Contacts 26 are formed by burying W or the like inthe contact holes. The contacts 26 are connected to the wirings 19.

Since the top insulating film 41 and side insulating film 42 (forexample, SiN films) and the interlayer insulating films 21 and 25 (forexample, SiO₂ films) are different materials, the etching selectivitybetween them is high. Each contact hole is formed adjacent to the writeword line WWL so as to expose the side surface of the side insulatingfilm 42. In this manner, the contact 26 can be formed in self-alignmentwith the side insulating film 42 and write word line WWL.

As shown in FIG. 22, a wiring 27 is formed on the contacts 26 andinterlayer insulating film 25, and an MTJ element film 23 is formed onthe wiring 27. A hard mask HM is formed on the MTJ element film 23 andpatterned. After that, the wiring 27 and MTJ element film 23 arepatterned into a desired shape. This forms wirings 27 and MTJ elementsMTJ having the same planar shape.

Finally, as shown in FIG. 16, the MTJ elements MTJ are buried with aninterlayer insulating film 28, and the interlayer insulating film 28 isplanarized until the hard masks HM are exposed. Subsequently, a wiring29 having a desired shape is formed on the interlayer insulating film 28and MTJ elements MTJ. The wiring 29 functions as a bit line BL.

[2-2] Modification Examples of Magnetic Random Access Memory (1)Modification Example 1

FIG. 23 is a sectional view showing modification example 1 of themagnetic random access memory according to the second embodiment.Modification example 1 of the magnetic random access memory according tothe second embodiment will be explained below.

As shown in FIG. 23, modification example 1 forms the write word lineWWL by the damascene process. Therefore, while the side insulating films42 are formed on only the side surfaces of the write word line WWL inthe structure shown in FIG. 16, an insulating film 52 formed on the sidesurfaces of the write word line WWL is also formed on the bottom surfaceof the write word line WWL in the structure shown in FIG. 23.

In the structure shown in FIG. 23, a barrier metal film 53 is desirablyformed between the write word line WWL and insulating film 52 in orderto ensure the reliability of a wiring. However, the barrier metal film53 need not always be formed. A top insulating film 54 is formed on thewrite word line WWL, barrier metal film 53, and insulating film 52. Theupper surface of the top insulating film 54 and that of the contact 26are in direct contact with the bottom surface of the wiring 27.

The contact 26 is formed in self-alignment with the insulating film 52and a bit line BL. Therefore, the side surface of the contact 26 is indirect contact with that of the insulating film 52.

The top insulating film 54 and insulating film 52 are desirably amaterial which increases the etching selectivity to an interlayerinsulating film 51 around them. Accordingly, when the interlayerinsulating film 51 is, for example, SiO₂, the top insulating film 54 andinsulating film 52 are preferably, for example, SiN films, AlxOy films,stacked films of SiN/Ta/NiFe/Ta, or FexOy films.

The top insulating film 54 is desirably thicker than the insulating film52. This is to allow the top insulating film 54 to adequately protectthe upper end portions and the like of the write word line WWL frombeing etched away during the formation of the contact 26.

FIGS. 24 to 28 are sectional views showing the manufacturing steps ofmodification example 1 of the magnetic random access memory according tothe second embodiment of the present invention. A method ofmanufacturing modification example 1 of the magnetic random accessmemory according to the second embodiment will be explained below.Although the damascene process of the write word line WWL will beexplained, other manufacturing steps are the same as those of the basicexample of the magnetic random access memory according to the secondembodiment described above.

First, as shown in FIG. 24, trenches 50 are formed in an interlayerinsulating film 51 of, for example, SiO₂ by selectively removing it byRIE or the like. An insulating film 52 is formed in the trenches 50 andon the interlayer insulating film 51. A barrier metal film 53 is formedon the insulating film 52. The insulating film 52 is, for example, SiN,and the barrier metal film 53 is a Ta-based material such as TaN. Awiring 22 made of Cu or the like is formed on the barrier metal film 53.After that, the wiring 22, barrier metal film 53, and insulating film 52are planarized by CMP or the like, thereby exposing the interlayerinsulating film 51.

Then, as shown in FIG. 25, a recess 55 is formed in the upper portion ofeach trench 50 by removing the upper portions of the wiring 22, barriermetal film 53, and insulating film 52.

As shown in FIG. 26, a top insulting film 54 is formed on the recesses55 and interlayer insulating film 51. The top insulating film 54 is, forexample, SiN.

As shown in FIG. 27, the top insulating film 54 on the interlayerinsulating film 51 is removed by CMP or the like, and left behind inonly the recesses 55.

As shown in FIG. 28, contact holes are formed in the interlayerinsulating film 51 by RIE or the like, and contacts 26 are formed byburying, for example, W in these contact holes. The contacts 26 areconnected to wirings 19 (not shown).

Since the top insulating film 54 (for example, an SiN film) andinsulating film 52 (for example, an SiN film) and the interlayerinsulating film 51 (for example, an SiO₂ film) are different materials,the etching selectivity between them is high. Each contact hole isformed adjacent to a write word line WWL so as to expose the sidesurface of the insulating film 52. In this manner, the contact 26 can beformed in self-alignment with the insulating film 52 and write word lineWWL.

As described above, modification example 1 forms the write word line WWLby the damascene process. This makes the MTJ element MTJ and write wordline WWL closer to each other than in FIG. 16. Accordingly, the writecurrent in the write word line WWL can be reduced.

(2) Modification Example 2

FIG. 29 is a sectional view of modification example 2 of the magneticrandom access memory according to the second embodiment of the presentinvention. Modification example 2 of the magnetic random access memoryaccording to the second embodiment will be explained below.

As shown in FIG. 29, the hard mask HM and bit line BL need not be indirect contact with each other, but may also be connected via a contact62. The contact 62 can be formed by forming a contact hole in aninterlayer insulating film 61, and burying a metal material in thiscontact hole.

Note that the contact hole 62 and bit line BL need not always be formedby separately burying metal materials. For example, the contact 62 andbit line BL can also be formed by forming a contact hole of the contact62 and a trench of the bit line BL, and simultaneously burying a metalmaterial in these contact hole and trench.

Modification example 2 as described above can achieve the same effect asthe structure shown in FIG. 16, and can also achieve the followingeffects by the formation of the contact 62. That is, modificationexample 2 can make the contact area between the MTJ element MTJ (hardmask HM) and bit line BL smaller than that in the structure shown inFIG. 16. This alleviates the influence of stress, and facilitatesmagnetic design. It is also possible to suppress etching damage to theMTJ element MTJ when the bit line BL is processed.

[2-3] MTJ Element

The MTJ element MTJ according to the second embodiment is the same asthat according to the first embodiment described previously, so anexplanation thereof will be omitted.

[2-4] Write Method

Similar to the write method according to the first embodiment, a writemethod according to the second embodiment uses one of magnetic fieldwrite and spin-transfer write.

The second embodiment differs from the first embodiment in thearrangement of the bit line BL and write word line WWL.

In the first embodiment, as shown in FIG. 2A, the bit line BL runs inthe magnetic hard axis direction of the MTJ element MTJ, and the writeword line WWL runs in the magnetic easy axis direction of the MTJelement MTJ. Since a write line running in the magnetic hard axisdirection of the MTJ element MTJ is the bit line BL, therefore, a writecurrent supplied to the bit line BL produces a magnetic field in themagnetic easy axis direction of the MTJ element MTJ. So, this writecurrent in the bit line BL desirably flows in both directions.

On the other hand, in the second embodiment, as shown in FIG. 17A, thewrite word line WWL runs in the magnetic hard axis direction of the MTJelement MTJ, and the bit line BL runs in the magnetic easy axisdirection of the MTJ element MTJ. Since a write line running in themagnetic hard axis direction of the MTJ element MTJ is the write wordline WWL, therefore, a write current supplied to the write word line WWLproduces a magnetic field in the magnetic easy axis direction of the MTJelement MTJ. So, this write current in the write word line WWL desirablyflows in both directions.

[2-5] Read Method

A read method according to the second embodiment is the same as the readmethod according to the first embodiment described above, so anexplanation thereof will be omitted.

[2-6] Effect

The second embodiment described above forms the contact 26, whichconnects the MTJ element MTJ and switching element, and the write wordline WWL in a region below the MTJ element MTJ. Also, the secondembodiment forms the contact 26 in self-alignment with the write wordline WWL, thereby implementing the structure in which the contact 26 isin direct contact with the side insulating film 42 of the write wordline WWL. That is, the second embodiment can decrease the cell sizebecause the contact 26 that connects the MTJ element MTJ and MOStransistor Tr can be formed adjacent to the write word line WWL. Morespecifically, as shown in FIG. 17A, letting F be the short side (thewidth in the magnetic hard axis direction) of the MTJ element MTJ and 2Fbe the long side (the width in the magnetic easy axis direction), a cellof 2F×3F=6F² can be implemented. This makes it possible to make the cellsize smaller than that in the first embodiment.

[3] Third Embodiment

In the third embodiment, the side insulating films and the like in thefirst and second embodiments are magnetic insulating films. For example,a magnetic insulating material is used to form the side insulating films24 shown in FIGS. 1 and 10, the side insulating films 42 shown in FIGS.16 and 29, and the insulating film 52 shown in FIG. 23.

Examples of this magnetic insulating material are insulating ferrite,and (Fe, Co)—(B, Si, Hf, Zr, Sm, Ta, Al)—(F, O, N)-based metal-nonmetalnano-granular films. More specifically, the insulating ferrite is atleast one of Mn—Zn-ferrite, Ni—Zn-ferrite, MnFeO, CuFeO, FeO, and NiFeO.

The third embodiment described above can achieve the same effects as thefirst and second embodiments.

In addition, in the third embodiment, a magnetic insulating film coversthe side surfaces of a bit line BL or write word line WWL. This magneticinsulating film achieves the effect as a yoke, and makes it possible toefficiently apply to a selected cell a current magnetic field generatedby the bit line BL or write word line WWL. Since this reduces the writecurrent, the power consumption can be reduced.

Also, since the magnetic insulating film covers the side surfaces of thebit line BL or write word line WWL, it is possible to more efficientlyinterrupt a leakage magnetic field to an adjacent MTJ element MTJ. Thissuppresses write errors.

Note that it is also possible to form a magnetic insulating film 71 onthe bottom surface of the write word line WWL as shown in FIGS. 30 and31, or on the bottom surface of the bit line BL as shown in FIGS. 32 and33. This makes it possible to more efficiently apply the write currentto a selected cell, thereby increasing the write current reducingeffect.

[4] Fourth Embodiment

The fourth embodiment is an example using a diode as a switchingelement.

FIGS. 34 and 35 are sectional views showing a magnetic random accessmemory according to the fourth embodiment of the present invention. Thismagnetic random access memory according to the fourth embodiment will beexplained below.

As shown in FIGS. 34 and 35, the difference from each embodimentdescribed above is that a diode D is used as a switching element insteadof a MOS transistor. The diode D is, for example, a p-n junction diodeand has a p-type diffusion layer 81 and n-type diffusion layer 82.

The above fourth embodiment can achieve the same effects as theindividual embodiments described above. In addition, the use of thediode D as a switching element eliminates the influence of the size of aMOSFET, so the cell density can further increase.

[5] Fifth Embodiment

The fifth embodiment is an example using a so-called “via hole process”or “dual damascene process” as the method of forming the contacts 26 andwirings 27 in each embodiment described above.

FIGS. 36A to 36C are schematic sectional views showing magnetic randomaccess memory manufacturing steps using the via hole process accordingto the fifth embodiment of the present invention. The via hole processaccording to the fifth embodiment will be briefly explained below.

As shown in FIG. 36A, a hole 26′ is formed in an interlayer insulatingfilm 25. Then, as shown in FIG. 36B, a metal material 90 consisting ofAlCu or the like is formed by sputtering to fill the hole 26′. As shownin FIG. 36C, the metal material 90 on the interlayer insulating film 25is processed by RIE. Consequently, a contact 26 and wiring 27 areformed.

FIGS. 37A to 37D are schematic sectional views showing magnetic randomaccess memory manufacturing steps using the dual damascene processaccording to the fifth embodiment of the present invention. The dualdamascene process according to the fifth embodiment will be brieflyexplained below.

As shown in FIG. 37A, a wiring trench 27′ is formed in an interlayerinsulating film 25. Then, as shown in FIG. 37B, a hole is formed in theinterlayer insulating film 25 from the bottom surface of the wiringtrench 27′, thereby forming a hole 26′. As shown in FIG. 37C, a metalmaterial 90 consisting of Cu or the like is formed by sputtering to fillthe wiring trench 27′ and hole 26′. As shown in FIG. 37D, the metalmaterial 90 is planarized by CMP until the interlayer insulating film 25is exposed. As a result, a contact 26 and wiring 27 are formed.

Note that FIGS. 36A to 36C and 37A to 37D are schematic views, so theshapes of the contact 26 and wiring 27 can be variously changed to beapplicable to each embodiment. It is of course also possible to add,around the contact 26 and wiring 27, an element (for example, the bitline BL shown in FIG. 1) existing in each embodiment.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A magnetic random access memory manufacturing method comprising:forming a switching element on a semiconductor substrate; forming afirst wiring above the switching element; forming, on the first wiring,a magnetoresistive effect element having a fixed layer, a recordinglayer, and a nonmagnetic layer formed between the fixed layer and therecording layer; forming a first side insulating film on side surfacesof the first wiring, and the magnetoresistive effect element; forming afirst interlayer insulating film covering the magnetoresistive effectelement; forming a first contact hole which exposes a portion of thefirst side insulating film; forming, in the first contact hole, a firstcontact connecting to the switching element; forming a second wiringabove the first contact and the magnetoresistive effect element toelectrically connect the magnetoresistive effect element and theswitching element by the second wiring; and forming a second interlayerinsulating film on the second wiring.
 2. The method according to claim1, wherein a side surface of the magnetoresistive effect element and theside surface of the first wiring are simultaneously processed.
 3. Themethod according to claim 1, further comprising forming a second contacthole in the first interlayer insulating film above the magnetoresistiveeffect element to connect the magnetoresistive effect element with thesecond wiring.
 4. A magnetic random access memory manufacturing methodcomprising: forming a switching element on a semiconductor substrate;forming a first wiring above the switching element; forming a topinsulating film on the first wiring; forming a first side insulatingfilm on side surfaces of the first wiring and the top insulating film;forming a first interlayer insulating film covering the first sideinsulating film and the top insulating film; exposing the top insulatingfilm by planarizing the first interlayer insulating film; forming acontact hole which exposes a portion of the first side insulating film;forming, in the contact hole, a first contact connecting to theswitching element; forming a second wiring on the first contact and thetop insulating film to electrically connect the second wiring and theswitching element; forming, on the second wiring, a magnetoresistiveeffect element having a fixed layer, a recording layer, and anonmagnetic layer formed between the fixed layer and the recordinglayer; and forming a third wiring above the magnetoresistive effectelement.
 5. A magnetic random access memory manufacturing methodcomprising: forming a switching element on a semiconductor substrate;forming a first wiring above the switching element by a damasceneprocess to form a first insulating film on side and bottom surfaces ofthe first wiring; forming a top insulating film on the first wiring andthe first insulating film; forming a first interlayer insulating filmcovering the top insulating film; exposing the top insulating film byplanarizing the first interlayer insulating film; forming a contact holewhich exposes a portion of the first insulating film; forming, in thecontact hole, a first contact connecting to the switching element;forming a second wiring on the first contact and the top insulating filmto electrically connect the second wiring and the switching element;forming, on the second wiring, a magnetoresistive effect element havinga fixed layer, a recording layer, and a nonmagnetic layer formed betweenthe fixed layer and the recording layer; and forming a third wiringabove the magnetoresistive effect element.